1. Field of the Invention
The present invention relates to a process for removing dissolved polynuclear aromatic hydrocarbons from an aqueous composition by inclusion complexation using a select group of water insoluble inclusion agents comprising an anchored cyclodextrin. More particularly, the present invention provides a process for reducing the concentration of polynuclear aromatic hydrocarbons in an aqueous refinery waste stream by contacting the stream with a bed comprising a water insoluble inclusion agent comprising an anchored cyclodextrin having an inclusion cavity diameter of at least about 10 angstroms under conditions which facilitate the selective formation of an inclusion complex between the polynuclear aromatic hydrocarbon and the cyclodextrin.
2. Objects of the Invention
Waste water produced by certain industrial processes often contains contaminants that are unique to the particular industry involved. In fact, The Clean Water Act of 1972 (CWA) mandates a two part approach to establish effluent limitations for industrial waste water. First, the Act mandates nationwide base-level treatment requirements based on an assessment of what is technologically and economically achievable for a particular industry. Second, the Act mandates more stringent requirements for specific plants where necessary to achieve water quality objectives for the particular body of water into which that plant discharges its waste streams. According to some commentators, Congress intended that the Environmental Protection Agency (EPA) implement this combination of standards in a way that would force control technology innovation.
Although the Act broadly defines pollutants subject to regulation and permitting, it furnished only limited guidance with regard to toxic pollutants. Accordingly, the EPA developed a policy which focused all of the regulatory mechanisms provided by the Act upon the effective regulation of toxic or priority pollutant discharges. In developing this policy the EPA identified the pollutants which would be the primary subject of regulation and the industries which would be the primary concern in applying the regulations. This policy was adopted by Congress as a blueprint for a toxics control strategy in 1977 and 1987 amendments to the Act.
Thus, Congress has established that certain pollutants are to be identified as "priority pollutants". These pollutants are subject to effluent limitations based on the best available technology. Polynuclear aromatic hydrocarbons are priority pollutants.
Since petroleum refinery processing operations result in the formation of polynuclear aromatic hydrocarbons, the petroleum refining industry is particularly affected by the designation of polynuclear aromatic hydrocarbons as priority pollutants. For example, hydrocracking which is a high severity hydroprocessing operation to decrease the molecular weight of hydrocarbonaceous materials is known to give rise to the formation of polynuclear aromatic hydrocarbons. U.S. Pat. No. 3,619,407 issued on Nov. 9, 1971 to Hendricks et al. describes a hydrocracking process which is hindered by the formation of a broad class of organic compounds known as polynuclear aromatic hydrocarbons and identified as "benzocorenenes". The reference describes the problems caused by the tendency of such compounds to plate out onto cooler surfaces. Accordingly, researchers in the field have focused their attention on means to remove polynuclear aromatic hydrocarbons from refinery product streams. For example, co-pending U.S. patent application Ser. No. 567,427, assigned to the assignee of the present invention discloses a process for the selective precipitation of stable polynuclear aromatic hydrocarbons from the heavy hydrocarbonaceous effluent stream derived from a hydrocracking operation. As a consequence of such separation methods some fraction of these pollutant materials ultimately finds a way into refinery waste water. Such waste water will likely contain a variety of undesirable materials, some of which will be priority pollutants. The priority pollutants, as discussed above, are generally subject to more stringent regulation and handling limitations. Thus, it would be highly desirable to selectively remove the priority pollutants for special treatment.
Accordingly, it is the principal object of the present invention to provide a process for selectively removing polynuclear aromatic hydrocarbons from an aqueous composition. This and other objectives are accomplished by the process summarized below.